1. Field of the Invention
The present invention relates to a solar cell.
2. Discussion of the Related Art
In recent years, with the expected exhaustion of the existing energy resources such as petroleum or coal, there is a growing interest in alternate energy sources which will substitute for existing energy resources. From among them, a solar cell is configured to generate electrical energy from solar energy, and it has been in the spotlight because solar energy can be easily obtained and has no problems with environmental pollution.
A typical solar cell includes a substrate and an emitter layer made of semiconductors having different conductive types such as a p type or an n type, and electrodes coupled to the substrate and the emitter layer. Here, a PN junction is formed at the interface of the substrate and the emitter layer.
When light is incident on the solar cell, a plurality of electron-hole pairs are generated from the semiconductors, and the generated electron-hole pairs are separated into electrons and holes (i.e., electric charges) by a photovoltaic effect. The electrons and the holes move toward the n-type semiconductor and the p-type semiconductor (e.g., the emitter layer and the substrate) and are collected by the electrodes electrically coupled to the substrate and the emitter layer. The electrodes are interconnected by electric wires, thereby allowing electric power to be obtained.
Here, one or more current collectors, such as bus bars coupled to the electrodes coupled to the emitter layer and the substrate, are placed over the emitter layer and the substrate. The current collectors function to move electric charges, collected by corresponding electrodes, to an external load through adjacent current collectors.
In this case, the current collectors are placed over not only the substrate on which light is not incident, but the emitter layer formed on a surface on which light is incident (i.e., a light-receiving surface). Accordingly, the efficiency of the solar cell is low because an area on which light is incident on the substrate is decreased by the current collectors.
In order to reduce the decrease in the efficiency of the solar cell resulting from placement of the current collectors on a light-receiving surface of the substrate, a metal wrap through (MWT) solar cell, etc., have been developed wherein the current collectors coupled to the emitter layer through via holes are placed on the rear surface of the substrate, placed on an opposite side to the light-receiving surface.